Can I use augmented data in the validation set?
You should not use augmented data in the validation nor in the test set.
Validation and test set are purely used for hyperparameter tuning and estimating the final performance, i.e. estimating the generalization error. These two data sets should be as close as possible to other data, which you could have acquired, but you actually haven not, i.e. your true data distribution.
It's fine to augment training data, since it mimics other samples from the true distribution by applying transformations, noise, etc. and thus helps to increase generalization performance (assuming your augmentation assumptions are right). But evaluation should always be performed on original data.